Light-transmitting, electrically conducting element



Jam 22, 1963 R. J. BLAZEK 3,074,816

LIGHT-TRANSMITTING, ELECTRICALLY CONDUCTING ELEMENT Filed Oct. 28, 1960FIG. I.

LIGHT-TRANSMITTING PLASTIC FIG. 2.

GLASS j United States Patent O 3,074,816 LIGHT-TRANSMITTNG, ELECTRICALLYCONDUCTING ELEMENT n Robert J. Blazek, Mendham, NJ., assigner toWestinghouse Electric Corporation, East Pittsburgh, Pa., a corporationof Pennsylvania Filed Det. 28, 196), Ser. No. 65,689 Claims. (Cl.117-211) This invention relates to light-transmitting, electricallyconducting elements and, more particularly, to such elements which haveboth a high degree of transparency and a relatively high electricalconductivity.

Electroluminescent devices are well known and usually comprise spacedelectrodes having phosphor and dielectric material includedtherebetween. When the phosphor is placed within the infiuence of analternating electric field, it serves to convert the electric iield intovisible radiations. In order to pass the radiations which are generated,at least one of the spaced electrodes which ybounds thephosphor-dielectric should be light transmitting. Electroluminescentdevices are usually fabricated on an inorganic foundation or substrateand a light-transmitting, -tin oxide electrode layer is normally formeddirectly on the inorganic substrate.

In the case the electroluminescent device is to be made flexible innature, or is required to be very resistant to shocks and impacts, it isdesirable to fabricate the supporting foundation or Isubstrate oflight-transmitting plastic material. The usual tin oxide electrodelayers cannot be placed on such plastic material, since the temperaturesof formation which are required to deposit such tin oxide electrodeswould decompose the plastic. Because of this, it has been necessary todevelop alternative light-transmitting electrode structures.

Light-transmitting electrode structures which have been used withplastic substrates include a iberglass mesh which has been previouslycoated with tin oxide. Metal mesh electrodes have also been used,wherein the generated light passes from the device through theinterstices of the mesh. In still another construction, gold has beenvacuum-deposited or sputtered onto the plastic foundation as acontinuous layer which is sufficiently thin to enable some of thegenerated light to be transmitted therethrough. Troubles have beenencountered with such gold electrodes, however, in that if a sufiicientamount of gold is deposited to achieve a desired value of conductivity,the light-transmitting characteristics of the coating suffer. It hasbeen disclosed in U.S. Patent No. 2,852,415, dated September 16, 1958,to improve a vacuum-deposited, light-transmitting, metallic coating byincorporating therein selected .amounts of selected dielectricmaterials. Of these additive dielectric materials, a small addition offerrie oxide to a gold coating has been found to be the best. Even withsuch ferric-oxide-modified gold conducting coatings, however, the lighttransmission has not been as good as desired.

It is the general object of this invention to avoid and overcome theforegoing and other diiculties of and objections to prior-art practicesby the provision of a lighttransmitting, electrically conducting elementwhich has both a high degree of transparency and a relatively highelectrical conductivity.

It is another object to provide compositions for lighttransmitting,electrically conduct-ing elements having improved performancecharacteristics.

It is a further object to provide light-transmitting, electricallyconducting elements which incorporate plastic substrates and which haveimproved performance characteristics.

The aforesaid objects of the invention, and other ob- Patented Jan. 22,1963 ICC jects which will become apparent as the description proceeds,.are achieved by providing on a light-transmitting substrate, animproved light-transmitting, electrically conducting coating or filmwhich consists essentially of gold and either tungsten oxide or amixture of tungsten oxide and iron oxide. There are provided permissibleand optimum proportions of tungsten oxide to gold, as well aspermissible and optimum proportions of tungsten and iron oxide to gold,if iron oxide is to be included in the coating iilm.

For a better understanding of the invention, reference should be had tothe accompanying drawings wherein:

FIG. 1 is a sectional elevational view of an electroluminescent devicewhich utilizes the improved lighttransmitting, electrically conductingelement of this invention;

FIG. 2 is a sectional elevational view of an alternative embodiment ofthe light-transmitting, electrically conducting element per se, whereinthe electrode film is formed as distinct film layers;

FIG. 3 is a sectional elevational view of another alternative embodimentfor the element per se, wherein the electrode films are somewhatmodified and are coated onto both sides of a plastic foundation by meansof intermediate, bonding polymer layers;

FIG. 4 is still another alternative embodiment for the element per se,wherein the electrode film is formed as a plurality of film layers.

The improved light-transmitting, electrically conducting element of thisinvention has utility with any device wherein such an element isrequired, an example being plastic, polarized goggles which are requiredto be electrically heated, in order to dispel fogging. The invention hasparticular utility with respect to electroluminescent devices, however,and hence it has been so illustrated and will be so described.

With specific reference to the form of the invention illustrated in thedrawings, the numeral 10 in FIG. 1 indicates generally anelectroluminescent cell which comprises a light-transmitting, plasticfoundation or substrate 12 with a light-transmitting and electricallyconducting first electrode layer or film 14 carried on a smooth surface16 of substrate 12. A phosphor-dielectric layer 18 is carried over thefilm 14 and a second electrode 20 is carried over thephosphor-dielectric layer 1S. An alternating electric potential isadapted to be applied across the electrodes 14 and 20, in order toenergize the device to light emission. The general construction of theelectroluminescent device 10 Iis conventional. As an example, thephosphor-dielectric layer 18 has a thickness of 2 mils and is formed ofiinely divided, copper-activated, zinc sulfide electroluminescentphosphor embedded in an equal part by weight of a light-transmittingdielectric plastic, such as polyvinyl chloride. The electrode 20 isformed of vacuum-metallized aluminum.

The light transmitting element of this invention is represented by theplastic substrate 12 and the electrode film 14. The substrate 12 can beformed of 'any suitable light-transrnitting plastic material such aspolymonochlorotriuoroethylene `and the flexibility of theelectroluminescent cell 1t is primarily determined by the flexibility ofthis substrate 12. As an example, the substrate has a thickness oli 10mils. Any suitable light-transmitting plastic can be used as thesubstrate, additional examples being acrylates, vinyls, polyethylene,polypropylene or polystyrene.

The electrode iilm 14 is shown in FIG. 1 in its preferred form. Thisfilm consists essentially of gold and either tungsten oxide or a mixtureof tungsten oxide and iron oxide. The surface of -this film 14, which isadjacent the smooth surface 16 of the substrate 12, 4is rich 3 in.tungsten oxide or a mixture of tungsten oxide and iron oxide. Theuppermost or other surface of the film 14 is rich in gold.

The ytungsten oxide and total metallic oxideY portion of 'the lfilm 14constitute from 1% to 20% by weight of the gold portion of .the film4and if iron oxide is included in 4the lm, it should constitute less`than 10% by Weight ofthe gold portion of the film. ln the preferredcornposition, ferric oxide and tungsten oxide are mixed and eachconstitutes about 4% by weight of the gold portion of Ithe film 14. lfonly tungsten oxide is to be used as the additive dielectric material,the preferred addition is about 8% by weight of the gold in the film. lfless than 1% by weight of additive dielectric material is used in thefilm, the improved performance characteristics for the film are notrealized. lf more than 20% by weight of additive dielectric material i-sused, the formed film has an appreciable gray body color which cuts downon transmitted light. Tungsten trioxide is the preferred additivetungsten oxide. The dioxide can be used, however, as can mix-tures ofthe trioxide and 'the dioxide. In addition, `oxides of iron other thanferrie oxide can be used. The term tungsten oxide and iron oxide as usedherein are intended to lbe gener-ic to any single oxide or mixture ofsuch oxides.

In forming the electrode film 14 on the smooth surface 16 of thefoundation 12, gold and tungsten oxide are placed into an electricallyheated boat. Preferably, iron oxide is also included in the boat. Theboat is placed into a conventional vacuum-deposition apparatus and theIsmooth surface 16 of the substrate 12 is placed proximate theelectrically heated boat. When the yapparatus is evacuated and the boatis heated, the iron .and tungsten oxides wlll tend to deposit first. Theinitial vacuum deposition of the -gold will be `somewhat limited. Aftersubstantially all of the iron and tungsten oxides have been volatilizedfrom the boat, the remainder of the gold will be volatilized. There willbe consideralbe mixing of the deposited materials at their interface,however, so that the ultimate film will be graded with respect to itscomposition, with ,the first-deposited surface being rich in the oxidesand the last-deposited surface being rich in gold. The vacuum-depostiionapparatus and boats are conventional and are not shown.

As a specific example flor forming the electrode film 14, 0.003 gram `oftungsten oxide and 0.003 gram of iron oxide, both in finely dividedform, are placed into a tungsten deposition boat with 0.080 gram ofgold. The boat has dimensions of 5.4 cm. by 1.0 cm. 4and a depth of 0.15crn. and is adapted to be electrically heated. The smooth surface 16 ofthe substrate 12 is placed 30 cm. from this boat and the system isevacuated to a pressure of 0.05 micron mercury. The -area of the surface16 of substrate 12 is 320 sq. cm. and it is centrally disposed directlyover lthe boat. The boat is rapidly heated to a temperature of 1200" C.,at which point the iron and tungsten oxides will volatilize, along witha limited amount of the gold. Heating is continued at this indictaedternperature and -mantained until the gold is substantially volatilized.The thickness of the deposited film will vary, depending upon thedesired conductivity and light-transmis-sion characteristics. As ageneral rule, however, the `thickness of the gold, if it were to bedeposited by itself, would be in the order of from 50 to 200 Angstromsand the lthickness of the iron and vtungsten oxides, if deposited bythemselves, would be in the order of from to 50 Angstroms. With filmsdeposited in accordance with .the foregoing specific example, theresistivity will be approximately to 20 ohms per square and the light-transmission ofthe films per se will be greater than 70%.

If it is desired to increase the resistivity of the electrode film, lessmaterial is deposited and, of course, the transmission characteristicswill be improved. Such films have use in polarized goggles, as indicatedhereinbefore.

In FIG. 2 is'shown an alternative embodiment 22 for thelight-transmitting element 10, as shown in FIG. 1. This alternativeembodiment 22 utilizes a glass substrate Z4. The electrode film 26 whichis carried on the substrate 24 is quite similar to the film 14, as shownin FIG. 1, except that the gold and metallic oxide or oxides aredeposited as discrete films. in forming the film 26, the iron andtungsten oxides are placed into one deposition boat and the gold isplaced into Ia separate deposition boat. The boat containing thetungsten oxide or iron and tungsten oxides is heated first, in order todeposit Ithe-se oxides completely before any gold is vacuum deposited.Thereafter the gold-containing boat is heated to vacuum deposit the goldonto the previously deposited oxide or oxides. This will form arelatively sharp line of delineation between the oxide film portion 26aand the gold film portion 26e.

in FlG. 3 is shown another yalterntaive embodiment 28 wherein the4substrate 12 is plastic as in the embodiment 10, shown in FfG. l.Separate films 30 are deposited on oppositely disposed faces of thesubstrate 12. The elect-rode films 30 are also modified in that the goldand additive oxides are generlaly uniformly mixed. Vln depositing suchfilms, the tungsten oxide or mixture of tungsten oxide and iron oxideare placed into one vacuum-deposition boat and the gold is placed intoanother vacuum-deposition boat. T-hese boats are simultaneously heatedin such manner that the metallic oxides and gold will volatilizesimultaneously, `thereby forming a generally uniformv deposited mixtureof gold and metallic oxide. 'Phe proportions of oxide to gold in each ofthe films 30 are as described in the previous embodiments. Theernbodiment 28 is also modified somewhat in that additionallight-transmitting, polymer layers 32 are provided between the smooth,oppositely disposed surfaces of the substrate 12 and the adhering films30. Such additional polymer layers are described in copendingapplication S.N. 65,690, filed concurrently herewith, titledElectroluminescent Device, Conducting Element and Method, by Robert J.Blazek, and owned by the .present assignee.

In FIG. 4 is shown yet another alternative embodiment for alight-transmitting, electrically conducting element 34, wherein themetallic oxide or oxides, as specified hereinbefore, are first depositedto form a layer 36 which is adjacent the smooth surface 16 ofthesubstrate 12.V Thereafter, a gold film 38 is deposited onto thefirst-deposited metallic oxide film 36 and an additional metallic oxidelrn 40, similar to those `specified hereinbefore, is deposited onto thegold film 38. To prevent abrasion, an additional thin layer 42 oflight-transmitting plastic, such as polyvinyl chloride, is provided overthe oxide film 40. In depositing the films 36, 38 and `40, twovacuum-deposition boats are used and the temperatures of these boats arecontrolled so as to deposit the multiple films. The tungsten oxide inthe first film 36 constitutes at least 1% by weight of the gold whichforms the second deposited film 38. The tungsten oxide in thethird-deposited metallic oxide film 40 also constitutes at least 1% byweight of the gold which is deposited to form the film 38. The combineddeposited oxide films 36 and 40 constitute from 2% to 20% by weight ofthe gold film 38, with the total iron oxide in these films 36 and 40constituting less than 10% by weight of the gold film 38. One advantageof such a construction is that the outermost film of metallic oxideslightly improves the light transmission characteristics of thecomposite film.

The best previously known, light-transmitting, electrically conductingcoatings which could be deposited on plastic have been those formed ofgold, as modified with a small addition of iron oxide. When the tungstenoxide is used to replace the iron oxide in the film, the transmission isimproved by approximately 3 to 4%, with the conductivity maintained thesame. Alternatively, if the same transmission is to be achieved, theresistivity of the tungsten-oxide-modified gold film, as expressed inohms per square, is approximately half that of the iron-oxidemodifiedgold lms. As representative values, if the transmissions of both thetungsten-oxide-modified gold film and the iron-oxide-modified gold filmare to be maintained at about 67%, the resistivity of thetungsten-oxidemodied film Will be 11 ohms per square and the resistivityof the iron-oxide-modified film will be approximately 23 ohms persquare.

The preferred conducting film, which will provide best transmission andconductance characteristics, is that in which mixed tungsten and ironoxides, as specified hereinbefore, are used. The transmission of thecombined oxide-modified coatings is approximately 8% greater than theiron-oxide-modified coating, when the resistivity of the films, asexpressed in ohms per square, is approximately the same.

The mechanism by which the added dielectric material serves to enhancethe conductivity of the conducting, vacuum-deposited gold films is notclearly understood. Apparently when the gold is deposited onto or withthe dielectric oxide materials as specied, the individual gold particlesdisplay a minimum of aggregations, thereby increasing the conductivitywhich is obtained for any given amount of deposited gold. If a similaramount of gold, per se, were to be deposited, the conductivity would notbe as good. If a sufiicient amount of gold, per se, were to be depositedto achieve a conductivity of l to 20 ohms per square, for example, thetransmission through such a deposited conducting film would berelatively poor.

The foregoing embodiments for the lighttransmitting, electricallyconducting articles, as shown in FIGS. 1-4 and as describedhereinbefore, are subject to considerable modification. As an example,any of the present electrode film embodiments, as specified, can beplaced on one or both sides of a light-transmitting substrate. This istrue for both glass and plastic substrates. Such constructions haveutility for forming multiple-layer electroluminescent devices. Also, anyof the embodiments which utilize a plastic substrate can incorporateintermediate polymer layers, in order to improve the adherence of theconducting films to the substrate. in such case, the polymer layersessentially form a part ofthe light-transmitting substrate. Further, anyof the embodiments can be provided With an exterior film formed of thedielectric metallic oxide, such as the film 40 as shown in FIG. 4.

As a further alternative construction, additional thin films of materialcan be used to grade the refractive index between the exterior filmsurface and the atmosphere. An example of such an additional film ismagnesium fluoride which has a relatively low index of refraction.Another example is a suitable plastic film, such as lighttransmittingfilm of polyvinyl chloride. As still another alternative, the conductingfilms, as specified hereinbefore, can be deposited by sputtering,although vacuum deposition is preferred because of the ease of control.

It will be recognized that the objects of the invention have beenachieved by providing an improved light-transmitting, electricallyconducting element which has both a high degree of transparency and goodelectrical conductivity. Compositions or such elements have beenprovided and these elements can be deposited onto plastic substrates.

While best embodiments of the invention have been illustrated anddescribed hereinbefore, it is to be particularly understood that theinvention is not limited thereto or thereby.

I claim:

l. An electrically conducting light-transmitting article comprising, alight-transmitting electrically insulating substrate having a smoothsurface, an electrically conducting light-transmitting continuous filmsupported on the smooth surface of said substrate, said film consistingessentially of gold and one additive material of the group consisting oftungsten oxide and a mixture of tungsten oxide and iron oxide, the totaladditive oxide portion of ti said film constituting from 1% to 20% byweight of the gold portion of said film, the tungsten oxide portion ofsaid film constituting at least 1% by weight of the gold portion of saidfilm, and iron oxide included in said film constituting less than 10% byweight of the gold portion of said film.

2. An electrically conducting light-transmitting article comprising, alight-transmitting electrically insulating plastic substrate having asmooth surface, an electrically conducting light-transmitting continuousfilm supported on the smooth surface of said substrate, said filmconsisting essentially of gold and a mixture of tungsten oxide and ironoxide, the total additive oxide portion of said film constituting from1% to 20% by weight of the gold portion of said film, the tungsten oxideportion of said film constituting at least 1% -by weight of the goldportion of said film, and the iron oxide included in said filmconstituting less than 10% by weight of the gold portion of said film.

3. An electrically conducting light-transmitting article comprising, alight-transmitting electrically insulating plastic substrate having asmooth surface, an electrically conducting light-transmitting continuousfilm supported on the smooth surface of said substrate, said filmconsisting essentially of gold and tungsten oxide, and the tungstenoxide portion of said film constituting from 1% to 20% by weight of thegold portion of said film.

4. An electrically conducting light-transmitting article comprising, alight-transmitting electrically insulating plastic substrate having asmooth surface, an electrically conducting light-transmitting continuousfilm supported on the smooth surface of said substrate, said filmconsisting essentially of gold and a mixture of tungsten trioxide andferrie oxide, the total additive oxide portion of said film constitutingfrom 1% to 20% by Weight of the gold portion of said film, the tungstentrioxide portion of said film constituting at least 1% by Weight of thegold portion of said film, and the ferric oxide included in said filmconstituting less than 10% by Weight of the gold portion of said film.

5. An electrically conducting light-transmitting article comprising, alight-transmitting electrically insulating plastic substrate having asmooth surface, an electrically conducting light-transmitting continuousfilm supported on the smooth surface of said substrate, said filmconsisting essentially of a mixture of gold and one additive material ofthe group consisting of tungsten oxide and a mixture of tungsten oxideand iron oxide, the total additive oxide portion of said filmconstituting from 1% to 20% by Weight of the gold portion of said film,the tungsten oxide portion of said film constituting at least 1% byweight of the gold portion of said film, and any iron oxide included insaid film constituting less than 10% by weight of the gold portion ofsaid film.

6. An electrically conducting light-transmitting article comprising, alight-transmitting electrically insulating substrate having a smoothsurface, electrically conducting light-transmitting continuous filmssupported on the smooth surface of said substrate, said filmscomprising, a first film adjacent the smooth surface of said substrateand selected from one material of the group consisting of tungsten oxideand a mixture of iron oxide and tungsten oxide, a second film overlyingsaid first film and consisting essentially of gold, said first filmconstituting from 1% to 20% by Weight of said second film, the tungstenoxide included in said first film constituting lat least 1% by weight ofsaid second film, and any iron oxide included in said first filmconstituting less than 10% by Weight of said second film.

7. An electrically conducting light-transmitting article as specified inclaim 6, wherein a third film overlies said second film, said third filmselected from one material of the group consisting of tungsten oxide anda mixture of iron oxide and tungsten oxide, said third film constitutingat least 1% by weight of said second film, said first and third filmsconstituting lfrom 2% to 20% by Weight of said second film, the tungstenoxide included in said third film constituting at least 1% by weight ofsaid second fi-lm, and any iron oxide included in said first and thirdfilms constituting less than 10% by weight of said second film.

8, An electrically conducting light-transmitting article comprising, alight-transmitting electrically insulating substrate having oppositelydisposed smooth surfaces, electrically conducting light-transmittingcontinuous lms supported on the oppositely disposed smooth surfaces ofsaid substrate, said films consisting essentially of gold and oneadditive material of the group consisting of tungsten oxide and amixture of tungsten oxide and iron oxide, the total additive oxideportion of each of said films constituting from 1% to 20% by Weight ofthe gold portion of said films, theV tungsten oxiderportion of each ofsaid films constituting at least 1% by Weight of the gold portion ofeach of said films, and any iron oxide included in each of said filmsconstituting less than 10% by Weight of the gold portion of said films.

9. An electrically conducting light-transmitting article comprising, alight-transmitting electrically insulating substrate having a smoothsurface, an electrically conducting light-transmitting continuous filmsupported on the smooth surface of said substrate, said film consistingessentially of gold and one additive material of the group consisting oftungsten oxide and a mixture of tungsten oxide and iron oxide, thesurface of said film adjacent the smooth surface of said substrate beingrich in material of said group and the other surface of said film beingrich in gold,` the additive oxide portion of said film constituting from1% to 20% by Weight of the gold portion of said film, the tungsten oxideportion of said film constituting at least 1% by Weight of the goldportion of said film, and any iron oxide included in said filmconstituting less than 10% by Weight of the gold portion of said film.

10. An electrically conducting light-transmitting article as specifiedin claim 9, wherein an additional film overlies said metallic oxide-goldfilm, said additional film selected from one material of the groupconsisting of tungsten oxide and a mixture of iron and tungsten oxides,the tungsten oxide in said additional film constituting at least 1% byweight of the gold in said metallic oxide-gold film, the total materialof said group included in said metallic oxide-gold film and saidadditional film constituting from 2% to 20% by Weight of the gold insaid metallic oxideagold film, and any iron oxide included in said filmsconstituting less than 10% by weight of the gold in said metallicoxide-gold film.

References Cite-xi in the file of this patent UNlTED STATES PATENTS

1. AN ELECTRICALLY CONDUCTING LIGHT-TRANSMITTING ARTICLE COMRPISING, ALIGHT-TRANSMITTING ELECTRICALLY INSULATING SUBSTRATE HAVING A SMOOTHSURFACE, AN ELECTRICALLY CONDUCTING LIGHT-TRANSMITTING CONTINUOUS FILMSUPPORTED ON THE SMOOTH SURFACE OF SAID SUBSTRATE, SAID FILM CONSISTINGESSENTIALLY OF GOLD AND ONE ADDITIVE MATERIAL OF THE GROUP CONSISTING OFTUNGSTEN OXIDE AND A MIXTURE OF TUNGSTEN OXIDE AN IRON OXIDE, THE TOTALADDITIVE OXIDE PORTION OF SAID FILM CONSTITUTING FROM 1% TO 20% BYWEIGHT OF THE GOLD PORTION OF SAID FILM, THE TUNGSTEN OXIDE PORTION OFSAID FILM CONSTITUTING AT LEAST 1% BY WEGHT OF THE FOLD PORTION OF SAIDFILM, AND IRON OXIDE INCLUDED IN SAID FILM CONSTITUTING LESS THAN 10% BYWEIGHT OF THE GOLD PORTION OF SAID FILM.